Field of the Invention
The present invention relates to a bending portion for an endoscope and an endoscope, and specifically relates to a bending portion for an endoscope which is formed by coupling a plurality of bending pieces in a rotatable manner, and the endoscope.
Description of the Related Art
A bending portion for an endoscope is configured by arraying a plurality of cylindrical bending pieces, which are called angle pieces or joint rings, in an axis direction of an inserting portion of the endoscope and rotatably connecting coupling leaves formed at end portions of adjacent bending pieces through a shaft such as a rivet pin.
A plurality of operation wires to perform a bending operation of the bending portion are inserted through the inside of the inserting portion of the endoscope, and these operation wires are inserted through wire receiving members provided in the bending pieces inside the bending portion. The distal end portions of these operation wires are fixed to the bending pieces arranged in the forefront of the bending portion, and the proximal end portions of these operation wires are attached to a bending operation member of a hand operating portion connected with the proximal end portion of the inserting portion. A plurality of bending pieces are rotated around a rivet pin by a push-pull operation of the operation wires by the bending operation member, and the bending portion is bent up to a position in which the end portions of adjacent bending pieces abut on each other. That is, the bending portion is designed such that the position in which the end portions of adjacent bending pieces abut on each other is in a mode in which the bending portion bends most greatly.
By the way, for example, a transnasal endoscope among endoscopes is especially requested to have a smaller outer diameter of the inserting portion and a larger diameter of a forceps channel to be inserted through the inserting portion. To meet such a request, it is forced to thin bending piece's thickness. However, when the bending piece's thickness is thinned, a phenomenon that the end portion of one bending piece gets into or onto the inside of the other bending piece because of low rigidity of the end portions of the bending pieces at the maximum bend state where the bending portion is bent most greatly, that is, a phenomenon called piece fall becomes likely to occur.
Moreover, if the end portions of adjacent bending pieces are mutually accurate circles of the same diameter, piece fall can easily occur after the end portions of the bending pieces abut on each other. When piece fall occurs, since the bending portion rapidly bends over a design value, there is a fear that built-in components such as an optical fiber, a forceps channel and a signal cable, which are inserted through the inside of the bending portion, are damaged, the decrease in durability of the bending pieces themselves is caused, and the degradation or the like of the bent shape of the bending portion is caused.
It is possible to decrease the occurrence frequency of piece fall by thickening the thickness of bending pieces, but it is not preferable because it leads to a larger diameter of the bending portion and an increase in the filling rate of built-in components under the above-mentioned request.
Therefore, the techniques of Japanese Patent Application Laid-Open Nos. 2000-316797, 2008-278969, and 2009-285085 shown below are disclosed as prevention measures of piece fall.
According to a bending portion of an endoscope disclosed in Japanese Patent Application Laid-Open No. 2000-316797, if the end edges of adjacent bending pieces do not abut on each other near the end edges of the adjacent bending pieces, piece fall is prevented by providing a projecting part, on which the end edge of one bending piece abuts, in the other bending piece. The projecting part of Japanese Patent Application Laid-Open No. 2000-316797 is provided in a belt shape along a circumferential direction on the outer peripheral surface of the bending piece.
According to a bending portion of an endoscope disclosed in Japanese Patent Application Laid-Open No. 2008-278969, piece fall is prevented by providing a projecting portion that is positioned on an axis in the bending direction of the bending portion and projects toward an inside of a bending piece, and by making projecting portions of adjacent bending pieces have different shapes from each other. As the shape of the projecting portion of Japanese Patent Application Laid-Open No. 2008-278969, for example, in the proximal-end-side end edge of a bending piece on the distal end side, there is provided a projecting portion which has a large curvature radius and projects toward the central axis, in the upper and lower portions of the outer peripheral wall at a position biased to one side across the axis line of the bending piece. Moreover, in the distal-end-side end edge of a bending piece on the proximal end side, there is provided a projecting portion which has a small curvature radius and projects toward the central axis, in the upper and lower portions of the outer peripheral wall at a position biased to the other side across the axis line of the bending piece.
According to a bending portion of an endoscope disclosed in Japanese Patent Application Laid-Open No. 2009-285085, by substantially matching the position of the proximal end portion of a distal end forming member and the position of the proximal end portion of the first bending piece in the axis direction of the inserting portion, a thick cylindrical portion is formed with the proximal end portion of the distal end forming member and the proximal end portion of the first bending piece. By this means, when an operating member (operation wire) is moved back and forth to make the bending portion perform bending operation, the proximal end surface of the thick cylindrical portion and the distal end surface of the second bending piece next to the distal end abut on each other. By this means, the piece fall of the second bending piece with respect to the first bending piece is prevented.